Logins from Dashlane or Roboform has nothing to do with Firefox Browser that is up to their support to handle those questions. Sounds like your passwords for firefox account is incorrect or you forgot it. And that would most likely prevent you from changing the password as well since that will be asked when you change your make a new password to confirm. You need to go and find out what was the password before signing off the working login otherwise that is considered a Lost Password and no one on Firefox forum end user help can help with that.